Thyroid Ultrasound Strategy Identifies Low-Risk Patients Who Can Defer Biopsy
In a study reported in JAMA Internal Medicine, Smith-Bindman et al evaluated the ability of ultrasound imaging characteristics to determine risk of thyroid cancer associated with thyroid nodules. They found that a strategy of using two abnormal nodule characteristics as an indication for biopsy could identify low-risk patients in whom biopsy could be deferred.
Study Details
This retrospective case-control study involved consecutive patients who underwent thyroid ultrasound imaging between January 1, 2000, and March 30, 2005. Thyroid cancers were identified through linkage with the California Cancer Registry.
Of a total of 8,806 patients who underwent 11,618 thyroid ultrasound examinations, 105 were diagnosed with thyroid cancer. Of these, 96 cancer patients and 369 controls formed the study group. There were no significant differences between groups in age or sex distribution. Nodules in control patients (n = 428) and benign nodules in cancer patients (n = 87) were pooled to form the control group of benign nodules (n = 515). Cancer patients had a total of 102 malignant nodules. Three cancer patients (3%) did not have nodules > 5 mm on ultrasound.
Independent Predictors of Cancer
Nodules were identified in 96.9% of cancer patients and 56.4% of control patients. On single-predictor modeling, microcalcifications had the strongest association with cancer, with coarse calcifications, nodule composition, nodule echogenicity, central vascularity, margins, and shape also being significantly associated with cancer.
On multiple-predictor modeling, only microcalcifications (odds ratio [OR] = 8.1, 95% confidence interval [CI] = 3.8–17.3), size > 2 cm (OR = 3.6, 95% CI = 1.7–7.6), and entirely solid composition (OR = 4.0, 95% CI = 1.7–9.2) were significantly associated with cancer.
Optimal Strategy Uses Any Two Abnormalities
If any one of these three characteristics were used as an indication for biopsy, most cases of thyroid cancer would be detected but with a high false-positive rate. For this strategy, sensitivity was 88%, the false-positive rate was 44%, and the positive likelihood ratio was 2.0; 56 biopsies would be needed per cancer case diagnosed and a negative result would be associated with a risk of cancer of 2 in 1,000 patients. If any two characteristics were required for biopsy, sensitivity would decrease to 52%, but the false-positive rate would decrease to 7%, and the positive likelihood ratio would increase to 7.1; only 16 biopsies would be needed per cancer case diagnosed and a negative result would be associated with a risk for cancer in 5 of 1,000 patients.
With regard to other potential strategies, use of microcalcification or solid nodule and nodule > 2 cm was associated with sensitivity of 54%, a false-positive rate of 8%, and a positive likelihood ratio of 6.7, with 17 biopsies needed per cancer case diagnosed. If presence of all three characteristics was required, sensitivity was only 7%, the false-positive rate was 0%, and the positive likelihood ratio was 28, with only 1 biopsy needed per cancer case diagnosed but most cases of cancer being missed.
The authors noted that compared with existing guidelines recommending biopsy of all thyroid nodules > 5 mm, use of the more stringent strategy requiring two abnormal characteristics would reduce unnecessary biopsies by 90% while maintaining a low risk of cancer in patients in whom biopsy is deferred.
The investigators concluded, “Thyroid ultrasound imaging could be used to identify patients who have a low risk of cancer for whom biopsy could be deferred. On the basis of these results, these findings should be validated in a large prospective cohort.”
Rebecca Smith-Bindman, MD, of the University of California, San Francisco, is the corresponding author for the article in JAMA Internal Medicine.
The study was supported by the California Department of Public Health, the National Cancer Institute's Surveillance, Epidemiology and End Results Program, and the Centers for Disease Control and Prevention's National Program of Cancer Registries. The study authors reported no potential conflicts of interest.
The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.
